1. Field of the Invention
This invention relates to a display device for indicating various kinds of informations, and more particularly to a display device having a deactuating or actuating switch for making the device inoperative or operative.
2. Description of the Prior Art
It is well known that a display device for displaying a various information is made operative during a desired period by operating an actuating switch into the on-state. The operating switch is provided in order to prevent unnecessary loss of electric power supply. In a camera, the switch prevents obstruction of the view finder with the data, and prevents the data from adversely affecting other devices such as a photometric device by photo-coupling with each other.
However, the display device may be made inoperative by turning the switch off and the device. On the other hand the display may be used to indicate a warning. Accordingly, the operator can not find out be warned without operating the actuating switch.
The above described situation may occur in a photographic camera. Such a display device usually comprises an illuminant display unit consisting of light emitting diodes, and is positioned in the viewing field of the camera finder for indicating various kinds of conditions and exposure value informations.
Further, this display device usually has the above described actuating switch for making the display device operative only when the operator wants to view the displayed information. The electric power consumption of the display device is too high for a small camera battery.
Another reason why the switch is usually provided is that the continuous display disturbs the operator's framing operation and may influence the photometric result so on, when the camera's exposure metering is of TTC type, since the display device is positioned in a viewing field of the camera finder.
Accordingly, the actuating switch is operated so as to turn on only in a display mode, and otherwise to turn off. Such operation of the actuating switch, however, fails to warn of undesirable situation even if they have occurred. Thus the operator continues photographing without being aware of an improper condition and fails to take a good photograph.